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Eukaryotic Cell, March 2007, p. 421-429, Vol. 6, No. 3
1535-9778/07/$08.00+0     doi:10.1128/EC.00264-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Melanin Biosynthesis in the Maize Pathogen Cochliobolus heterostrophus Depends on Two Mitogen-Activated Protein Kinases, Chk1 and Mps1, and the Transcription Factor Cmr1 ^,

Noa Eliahu,¹ Aeid Igbaria,¹ Mark S. Rose,² Benjamin A. Horwitz,¹ and Sophie Lev^1*

Department of Biology, Technion-Israel Institute of Technology, Haifa, Israel,¹ Biopharma, Syngenta Biotechnology, Inc., 3054 Cornwallis Rd., Research Triangle Park, North Carolina 27709²

Received 17 August 2006/ Accepted 8 January 2007

The maize pathogen Cochliobolus heterostrophus requires two mitogen-activated protein kinases (MAPKs), Chk1 and Mps1, to produce normal pigmentation. Young colonies of mps1 and chk1 deletion mutants have a white and autolytic appearance, which was partially rescued by a hyperosmotic environment. We isolated the transcription factor Cmr1, an ortholog of Colletotrichum lagenarium Cmr1 and Magnaporthe grisea Pig1, which regulates melanin biosynthesis in C. heterostrophus. Deletion of CMR1 in C. heterostrophus resulted in mutants that lacked dark pigmentation and acquired an orange-pink color. In cmr1 deletion strains the expression of putative scytalone dehydratase (SCD1) and hydroxynaphthalene reductase (BRN1 and BRN2) genes involved in melanin biosynthesis was undetectable, whereas expression of PKS18, encoding a polyketide synthase, was only moderately reduced. In chk1 and mps1 mutants expression of PKS18, SCD1, BRN1, BRN2, and the transcription factor CMR1 itself was very low in young colonies, slightly up-regulated in aging colonies, and significantly induced in hyperosmotic conditions, compared to invariably high expression in the wild type. These findings indicate that two MAPKs, Chk1 and Mps1, affect Cmr1 at the transcriptional level and this influence is partially overridden in stress conditions including aging culture and hyperosmotic environment. Surprisingly, we found that the CMR1 gene was transcribed in both sense and antisense directions, apparently producing mRNA as well as a long noncoding RNA transcript. Expression of the antisense CMR1 was also Chk1 and Mps1 dependent. Analysis of chromosomal location of the melanin biosynthesis genes in C. heterostrophus resulted in identification of a small gene cluster comprising BRN1, CMR1, and PKS18. Since expression of all three genes depends on Chk1 and Mps1 MAPKs, we suggest their possible epigenetic regulation.

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* Corresponding author. Mailing address: Department of Biology, Technion-Israel Institute of Technology, Haifa, Israel. Phone: 972-48293544. Fax: 972-48225153. E-mail: sophia{at}tx.technion.ac.il.

Published ahead of print on 19 January 2007.

Supplemental material for this article may be found at http://ec.asm.org/.

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Eukaryotic Cell, March 2007, p. 421-429, Vol. 6, No. 3
1535-9778/07/$08.00+0     doi:10.1128/EC.00264-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

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